This invention relates to an improved bearing assembly for supporting the main and auxiliary countershafts in a manual transmission.
Prior art manual transmissions require that two shimming operations be applied on two bearing arrangements supporting the main and auxiliary shafts when the main and auxiliary countershafts are installed in the transmission housing. Shimming adjusts the tolerance along the shafts' axis so that the bearings do not wear too quickly. Typically, one end of the housing has a bearing that is grounded, or unshimmed, and which supports one end of the main shaft. The other end of the main shaft is supported at a housing center support by a bearing arrangement that must be shimmed before the auxiliary shaft may be installed.
This shimming operation is accomplished by preloading the main shaft to obtain the desired tolerance and determine the correct shim size to achieve that tolerance. Once shimmed, the bearing is fixed in the center support. The auxiliary shaft is then installed with one end supported in the center support. A preload is applied to the auxiliary shaft to obtain the desired tolerance and determine the ideal shim size for the auxiliary shaft. The other end of the auxiliary shaft must then be shimmed to ensure that the correct tolerance is obtained for the auxiliary shaft.
Thus, for a two shaft arrangement, all the bearings are fixed to the housing and each shaft is shimmed individually.